Internal combustion engines having a relatively small number of cylinders provide automobile makers with an attractive solution to the need for improved fuel economy. In order to compensate for the reduction of cubic capacity, vehicle manufacturers developed technologies to improve engine power, such as direct fuel injection, turbocharging, and variable timing for inlet and exhaust camshafts. In this way, six- and eight-cylinder engines can be scaled down without losing available horsepower.
An undesirable consequence of engines having higher cylinder pressures or a smaller number of cylinders is that the engine order torsionals increase. This can cause gear rattle in the transmission and increase interior NVH such as steering wheel vibration.
Engineers managed these vibrations to one extent or another through a variety of approaches, many of which increase the cost of construction and reduce fuel economy. One accepted solution to overcome excessive vibration is the provision of one or more pendulums on the crankshaft to lower the torsional vibration of the crankshaft and the consequent driveline and interior NVH. Such crankshaft-mounted pendulums function as vibration absorbers as they are tuned to address and thus cancel out vibrations generated by crankshaft rotation, thus smoothing torque output of the crankshafts. This approach is taken as well by designers of some airplane piston engines where the pendulums smooth output torque.
An example of a pendulum vibration absorber associated with an engine crankshaft is set forth in U.S. Pat. No. 4,739,679, assigned to the assignee of the instant application. According to the arrangement set forth in this patent, a pendulum includes an inner curved cam follower surface that is alternately engaged and disengaged from a pin type cam fixed on the pendulum carrier.
The crankshaft pendulum is interconnected with the pendulum carrier by pendulum rolling pins. Each pendulum rolling pin rides on a rolling path formed in the pendulum and in the carrier. The cycloid shape is itself difficult and expensive to machine. Instead of machining the shape, one solution is to use a near net shape powder metal insert which is less expensive to produce. The insert is press-fitted into the ear of the pendulum carrier. However, the required press to fit the inserts into position results in unacceptably high stresses in the area adjacent to the insert. Therefore this concept is not a practical solution in an actual manufacturing environment. An alternative approach is to provide a fully machined pendulum made of forged steel yields at the rolling pin contact. However, this approach is also impractical as expensive heat treatment and subsequent hard machining is required.
Accordingly, a new approach to forming rolling path inserts for use in pendulum crankshaft assemblies is needed to address the problems associated with known arrangements.